Electrostriction is a property of all electrical non-conductors, or dielectrics that causes them to change their shape under the application of an electric field. Magnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization. Electrostriction and magnetostriction can be used for actuation purposes, and today a large variety of transducers operate according to these basic principles. Due to a very simple and reliable structure, solid state actuators of this kind are made in large numbers for various Applications. As an example, they may replace step-motors in servo-systems or they may be used in many different control applications for exact positioning of light beams, mirrors, or valves, etc.
Typically a solid state actuator is very limited with regard to the ability to move an end effector relative to a base. Typically, it will be able to provide movement of the end effector within a very short range, typically with relative modest force, and typically, they have low kinematic capabilities. In fact, often they are only capable of conducting a linear movement in the direction of the expansion or compression.
Various attempts have been made to improve the range of movement, the force which can be exerted, or to improve the kinematic capabilities.
Bending actuators of solid state type have been used in different designs in multifarious applications in industry for many years. They are characterized by a small design format, low energy requirements, and high reliability. Thus, for example, a piezoelectric bending actuator exhibits a service life of at least 10.sup.9 cycles in the industrial environment. However, the kinematic capabilities are limited, and more particularly, the end effector of a solid state bender cannot move in a flat plane but only in a spherical plane.
In U.S. Pat. No. 7,026,745, an actuator is proposed with a laminate structure which provides deflection in two different directions when energised appropriately.
In US 2010/0156242, an actuator drive structure is proposed where two solid state elements cooperate to provide rotational movement of the end-effector.
In US 2007/0138915A1, a wobble motor is presented where a shaft is driven in rotation by a structure generally extending in a Z direction, bendable in two directions perpendicular to the Z direction. The active elements thereby have a narrow range of movement of the actuators, and the end-face of the structure becomes non-planar due to the bending.